Taking care of tendons

The horse’s leg tendons are held within a protective digital flexor tendon sheath. Oliver James MRCVS explains what it is and the common injuries it can sustain

- Oliver James

THE digital flexor tendon sheath (DFTS) is a compartment that contains the major flexor tendons: namely, the superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT). It produces a small quantity of synovial fluid which acts as a lubricant, allowing the tendons to move without friction across the pastern and fetlock joints as the horse moves, and helping to protect them from repetitive stresses and compressive forces.

Significantly, the sheath lies just under the skin and at places is less than 5mm from the surface of the skin. This leaves the tendons inside vulnerable to injury. Adding to this, tendons that sit outside tendon sheaths benefit from a thick protective tissue layer known as the paratenon, but those within the DFTS have no such layer surrounding them, which is one of the reasons why tendon injuries within the sheath do not heal as well or as quickly as those that occur outside it.

MAJOR ANATOMY

THE DFTS is found in all four of the horse’s limbs, and extends from the lower third of the cannon bone to the navicular bursa (a small, fluid-filled sac that acts like a cushion between tendons and bones) inside the hoof capsule, at the level of the short pastern.

The DFTS is separated into three anatomical zones:

• the proximal region (the bottom third of the cannon bone),
• the fetlock canal (around the back of the joint), and
• the distal region (the long pastern area).